High demands are made on internal combustion engines, in particular in motor vehicles. The pollutant emissions are subject to legal regulations and the customer demands low fuel consumption, safe and reliable operation and low maintenance costs. The fuel supplying device of the internal combustion engine has a strong influence on whether the demands may be met.
DE 199 16 101 A1 discloses a method and a device for controlling an internal combustion engine. A high-pressure pump conveys fuel from a low-pressure region into a fuel accumulator. An actual value of a fuel pressure in the fuel accumulator is detected. In a first operating state the high-pressure pump is controlled as an actuator to adjust the fuel pressure in the fuel accumulator. In a second operating state a pressure relief valve is controlled as an actuator to discharge fuel from the fuel accumulator into the low-pressure region to adjust the fuel pressure. In the first operating state a control deviation between a desired value of the fuel pressure and the actual value of the fuel pressure is supplied to a first regulator. In the second operating state the control deviation is supplied to a second regulator. The first regulator is only used if the control deviation is positive. The second regulator is only used if the control deviation is negative. A switch takes place between the first operating state and the second operating state if the respectively active regulator reaches a zero control point and the control deviation is greater than a first threshold or the control deviation is less than a second threshold.
A method for operating an internal combustion engine is also disclosed in WO 2004/104397 A1 in which, in a first operating mode, a fuel pressure in a fuel accumulator is regulated to a desired pressure by adjusting a flow of fuel from fuel supplied to the high-pressure pump as a function of a volume of fuel to be injected and the desired pressure, and in which, in a second operating mode, with a specified flow of fuel, the fuel pressure is regulated to the desired value by discharging fuel from the fuel accumulator. The second operating mode is adopted if the flow of fuel falls below a first flow of fuel and the first operating mode is adopted if the flow of fuel exceeds a second flow of fuel.